Microcontrollers may include a random number generator module. The random number generator module can generate random numbers based on an input from an entropy source. Variations in the entropy source may affect the randomness of the data generated by random number generator modules embedded in microcontrollers. Microcontrollers in the same series or from the same production lot may have fewer variations in their entropy sources and may exhibit less variation in the randomness in the data generated between random number generators included in microcontrollers in a series.